Shoe for swash plate type compressor

ABSTRACT

A shoe for a swash plate type compressor is disposed between a swash plate provided on a rotational shaft in an inclined manner, the swash plate being configured to be rotated together with the rotational shaft, and a piston configured to be reciprocated in a direction in which the rotational shaft extends, by means of the rotation of the swash plate. The shoe for swash plate type compressor includes a flat surface in contact with the swash plate, and a spherical surface in contact with a semispherical slide surface formed on the piston. A through-hole communicating the flat surface and the spherical surface with each other is formed between the flat surface and the spherical surface. The through-hole is composed of a first through-hole having a first diameter and a second through-hole having a second diameter that is larger than the first diameter.

TECHNICAL FIELD

The present invention relates to a shoe for swash plate type compressor in which occurrence of seizure between a swash plate and a piston can be prevented.

BACKGROUND ART

As shown in FIG. 5, a conventional swash plate type compressor includes: a housing 20; a rotational shaft 2 disposed in the housing 20, the rotational shaft 2 being configured to be rotated; a swash plate 5 provided on a periphery of the rotational shaft 2 in an inclined manner, the swash plate 5 being configured to be rotated together with the rotational shaft 2; a piston 7 receiving an outer peripheral edge of the swash plate 5, the piston 7 being configured to be reciprocated in a rotational shaft direction by means of the rotation of the swash plate 5; and a shoe 90 disposed between the swash plate 5 and the piston 7. The shoe 90 has a flat surface 92 in contact with the swash plate 5, and a spherical surface 91 slidably in contact with a semispherical slide surface 13 of the piston 7.

By reciprocating the piston 7 of the swash plate type compressor in the rotational shaft direction (direction indicated by the arrow M in FIG. 5), a frozen refrigerant (e.g., chlorofluorocarbon) is sucked into and discharged from the swash plate type compressor. The frozen refrigerant contains a small amount of mist of lubrication oil. The lubrication oil is supplied to a space between the swash plate 5 and the shoe 90, and to a space between the shoe 90 and the piston 7.

Since the swash plate 5 is slid while applying a large pressure to the shoe 90, a large frictional force is generated between the swash plate 5 and the shoe 90, so that seizure may possibly occur between the swash plate 5 and the shoe 90.

Even when a lubrication oil is supplied to the space between the shoe 90 and the piston 7, there is a possibility that the seizure might occur between the shoe 90 and the semispherical slide surface 13 of the piston 7, because of a frictional force generated between the shoe 90 and the semispherical slide surface 13 of the piston 7.

In order to cope with this problem, there have been known a shoe whose spherical surface is provided with a helical groove and a shoe whose spherical surface has a somewhat flattened top, in order to prevent occurrence of seizure between the shoe and a semispherical slide surface (see, for example, Patent Documents 1 and 2). In addition, there has been known a shoe whose flat surface has a circular recess or an annular groove formed in a center part thereof, in order to prevent occurrence of seizure between a swash plate and the shoe (see, for example, Patent Documents 3 and 4).

However, in the shoe used in the aforementioned conventional swash plate type compressor, since an oil lubrication effect is local, an amount of the lubrication oil between the swash plate and the shoe and/or between the shoe and the piston is insufficient, whereby there is a possibility that the oil lubrication effect is lost. Thus, the seizure may occur between the swash plate and the shoe and/or the seizure may occur between the shoe and the piston.

In addition, since such a shoe itself has a large weight, a large load is imposed on the piston and the swash plate, which is likely to cause abrasion. Thus, in order to reduce the weight of the shoe, there has been known a hollow shoe provided with a flat surface having a substantially constant thickness, and a spherical surface having a thickness that is gradually decreased toward a top (see Patent Document 5).

However, as shown in Patent Document 5, when the hollow shape is changed in order to make constant the thickness, the strength of the shoe lessens. Such a small-sized shoe is insufficient in durability and it is difficult to practically use the shoe. In addition, since the degree of the reduced weight is about 10% at the most, the effect of weight reduction is not yet sufficient.

-   Patent Document 1: JP11-50959A -   Patent Document 2: JP63-007288U -   Patent Document 3: JP Patent Publication No. 03-12671 -   Patent Document 4: JP Patent Publication No. 04-77155 -   Patent Document 5: JP2002-39058A

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstances. The object of the present invention is to provide a shoe for swash plate type compressor, the shoe being capable of preventing the seizure (burn) between the a flat surface of the shoe and a swash plate and the seizure between a spherical surface of the shoe and a piston. The shoe can be downsized, while maintaining an excellent durability.

A shoe for a swash plate type compressor according to the present invention is a shoe for swash plate type compressor, disposed between a swash plate provided on a rotational shaft in an inclined manner, the swash plate being configured to be rotated together with the rotational shaft, and a piston configured to be reciprocated in a direction in which the rotational shaft extends, by means of the rotation of the swash plate, the shoe for swash plate type compressor comprising:

a flat surface in contact with the swash plate; and

a spherical surface in contact with a semispherical slide surface formed on the piston;

wherein:

a through-hole communicating the flat surface and the spherical surface with each other is formed between the flat surface and the spherical surface; and

the through-hole is composed of a first through-hole of a cylindrical shape having a first radius and a second through-hole of a cylindrical shape having a second radius that is larger than the first radius.

In the shoe for a swash plate type compressor according to the present invention, the first through-hole may be formed on a side of the spherical surface so as to extend up to the spherical surface, and the second through-hole may be formed on a side of the flat surface so as to extend up to the flat surface.

The shoe for a swash plate type compressor according to the present invention may further comprises a transitional hole of a truncated conical shape formed between the first through-hole and the second through-hole, the transitional hole communicating the first through-hole and the second through-hole with each other.

In the shoe for a swash plate type compressor according to the present invention, an inner circumferential part of the flat surface adjacent to the through-hole may be inclined toward the spherical surface, and an inner circumferential part of the spherical surface adjacent to the through-hole may be inclined toward the flat surface.

In the shoe for a swash plate type compressor according to the present invention, the spherical surface may have a contact surface in contact with the slide surface of the piston under a static state, and a non-contact surface not in contact with the slide surface under the static state.

In the shoe for a swash plate type compressor according to the present invention, the flat surface may have a contact surface in contact with the swash plate under the static state, and an area of the contact surface of the spherical surface and an area of the contact surface of the flat surface may be substantially equal to each other.

According to the present invention, there is provided the cylindrical through-hole communicating the flat surface and the spherical surface with each other. The through-hole is composed of the cylindrical first through-hole having the first diameter, and the cylindrical through-hole having the second diameter larger than the first diameter. Thus, oil can be supplied to the flat surface and the spherical surface of the shoe, whereby the seizure (burn) between the flat surface of the shoe and the swash plate and the seizure between the spherical surface of the shoe and the piston can be prevented. In addition, the shoe can be downsized, while maintaining an excellent durability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1( a)(b) are sectional views showing an operation of a swash plate type compressor according to an embodiment of the present invention.

FIG. 2 is a side sectional view showing a shoe for swash plate type compressor according to an embodiment of the present invention.

FIG. 3 is a side sectional view showing the shoe for swash plate type compressor according to an alternative example of the embodiment of the present invention.

FIG. 4 is a view for explaining an example of the shoe for swash plate type compressor according to the embodiment of the present invention.

FIG. 5 is a sectional view showing a conventional swash plate type compressor.

EMBODIMENTS OF THE INVENTION

An embodiment of a swash plate type compressor and a shoe for swash plate type compressor according to the present invention will be described herebelow, with reference to the drawings. FIGS. 1( a) (b) to FIG. 4 are views showing the embodiment of the present invention. A shoe for swash plate type compressor 30 according to this embodiment can be used in, for example, an air compressor of an automobile or the like.

As shown in FIGS. 1( a) and 1(b), a swash plate type compressor includes: a housing 20; a rotational shaft 2 disposed in the housing 20, the rotational shaft 2 being configured to be rotated (in a direction indicated by the arrow C in FIGS. 1( a) and 1(b)); a swash plate 5 provided on a periphery of the rotational shaft 2 in an inclined manner, the swash plate 5 being configured to be rotated together with the rotational shaft 2; a piston 7 receiving an outer peripheral edge of the swash plate 5, the piston 7 being configured to be reciprocated in a direction in which the rotational shaft 2 extends, by means of the rotation of the swash plate 5; and a shoe for swash plate type compressor 30 (hereinafter also referred to merely as “shoe 30”) disposed between the swash plate 5 and the piston 7.

As shown in FIGS. 1( a) and 1(b), the housing 20 has a pair of cylinder blocks 1 a and 1 b which cover the piston 7 from a periphery thereof, a front cover 9 connected to one end of the cylinder block 1 a, and a rear cover 11 connected to the other end of the cylinder block 1 b. A first valve plate 8 a is disposed between the cylinder block 1 a and the front cover 9, and a second valve plate 8 b is disposed between the cylinder block 1 b and the rear cover 11. The pair of cylinder blocks 1 a and 1 b are connected to each other by a bolt (not shown).

As shown in FIGS. 1( a) and 1(b), the first valve plate 8 a is provided with a first discharge valve 21 a connected to a discharge pipe (not shown) for discharging a frozen refrigerant (e.g., chlorofluorocarbon), and a first suction valve 22 a connected to a suction pipe (not shown) to which a frozen refrigerant is supplied. The second valve plate 8 b is provided with a second discharge valve 21 b connected to a discharge pipe (not shown) for discharging a frozen refrigerant, and a second suction valve 22 b connected to a suction pipe (not shown) to which a frozen refrigerant is supplied. The frozen refrigerant contains a small amount of mist of lubrication oil. The lubrication oil is supplied to a space between the swash plate 5 and the shoe 30, and to a space between the shoe 30 and the piston 7.

As shown in FIGS. 1( a) and 1(b), the rotational shaft 2 is rotatably held on the cylinder blocks 1 a and 1 b through bearings 3 and 4. The rotational shaft 2 is connected to a drive unit (not shown) that drives the rotational shaft 2.

As shown in FIGS. 1( a) and 1(b), the pair of cylinder blocks 1 a and 1 b, the first valve plate 8 a, the second valve plate 8 b and the rotational shaft 2 constitute a compression chamber 6 accommodating therein the piston 7 that is reciprocated in the rotational shaft direction.

As shown in FIG. 2, the shoe 30 disposed between the swash plate 5 and the piston 7 has a flat surface 32 in contact with the swash plate 5, and a spherical surface 31 slidably in contact with a semispherical slide surface 13 formed on the piston.

As shown in FIG. 2, formed between the flat surface 32 and the spherical surface 31 of the shoe 30 is a through-hole 35 communicating the flat surface 32 and the spherical surface 31 with each other. The through-hole 35 is composed of a cylindrical first through-hole 36 having a first diameter d₁, and a cylindrical second through-hole 37 having a second diameter d₂ that is larger than the first diameter d₁.

As shown in FIG. 2, the first through-hole 36 is formed on a side of the spherical surface 31 so as to extend up to the spherical surface 31, and the second through-hole 37 is formed on a side of the flat surface 32 so as to extend up to the flat surface 32. Between the first through-hole 36 and the second through-hole 37, there is formed a transitional hole 38 of a truncated conical shape, which communicates the first through-hole 36 and the second through-hole 37 with each other.

In this embodiment, the transitional hole 38 is formed between the first through-hole 36 and the second through-hole 37, which is by way of example, and the present invention is not limited thereto. As shown in FIG. 3, the first through-hole 36 and the second through-hole 37 may be communicated with each other, without the transitional hole 38.

As shown in FIG. 2, an outer circumferential part of the flat surface 32 of the shoe 30 is chamfered so as to be inclined toward the spherical surface 31. The inclination angle θ is about 10° relative to a plane in parallel with the flat surface 32.

As shown in FIG. 2, an inner circumferential part of the flat surface 32 adjacent to the through-hole 35 is chamfered so as to be inclined toward the spherical surface 31. Similarly, an inner circumferential part of the spherical surface 31 adjacent to the through-hole 35 is chamfered so as to be inclined toward the flat surface 32.

As shown in FIGS. 1( a) and 1(b), the piston 7 has the semispherical slide surface 13. The spherical surface 31 of the shoe 30 is slidably held within the semispherical slide surface 13 of the piston 7.

As shown in FIG. 2, the spherical surface 31 of the shoe 30 has a contact surface 31 a and a non-contact surface 31 b. The contact surface 31 a is in contact with the semispherical slide surface 13 of the piston 7, when the swash plate type compressor is under a static state where it is not driven. The non-contact surface 31 b is not in contact with the semispherical slide surface 13 of the piston 7, when the swash plate type compressor is under the static state state where it is not driven. In this embodiment, a diameter D₁ between starting points of the contact surface 31 a, at which the shoe 30 starts to be in contact with the semispherical slide surface 13 of the piston, is about 6.00 mm, and a diameter D₂ between ending points of the contact surface 31 a, at which the shoe 30 ends to be in contact with the semispherical slide surface 13 of the piston is about 13.00 mm.

In this embodiment, the contact surface 31 a of the spherical surface 31 is located on a virtual spherical surface. A radius R₁ of the virtual spherical surface is about 9.00 mm. The non-contact surface 31 b has a surface which is substantially in parallel with the virtual spherical surface on which the contact surface 31 a is located, and is recessed from the virtual spherical surface.

As shown in FIG. 2, the flat surface 32 has a contact surface 32 a and a non-contact surface 32 b. The contact surface 32 a is in contact with the swash plate 5, when the swash plate type compressor is under the static state state where it is not driven. The non-contact surface 32 b is not in contact with the swash plate 5, when the swash plate type compressor is under the static state state where it is not driven.

Herein, it is preferable that an area of the contact surface 31 a of the spherical surface 31 and an area of the contact surface 32 a of the flat surface 32 are substantially equal to each other. When the area of the contact surface 31 a of the spherical surface 31 and the area of the contact surface 32 a of the flat surface 32 are substantially equal to each other, a pressing force per unit area applied between the semispherical slide surface 13 and the spherical surface 31, and a pressing force per unit area applied between the flat surface 32 and the swash plate 5, can be made substantially equal to each other. Thus, the shoe 30 can be slid in a well-balanced manner.

In order to make the area of the contact surface 31 a of the spherical surface 31 and the area of the contact surface 32 a of the flat surface 32 be substantially equal to each other, the diameter D₂ between the ending points of the contact surface 31 a is adjusted and/or the diameters d₁ and d₂ of the through-hole 35 are adjusted.

A diameter d₃ of the contact surface 32 a of the flat surface 32 of the shoe 30 is about 13.00 mm, a height H of the shoe 30 is about 5.85 mm, and a diameter d₄ of the shoe 30 is about 15.00 mm (see FIG. 2).

It is preferable that the diameter d₁ of the first through-hole 36 of the through-hole 35 is about 30% to about 45% of the radius R₁ of the virtual spherical surface. It is preferable that the diameter d₂ of the second through-hole 37 of the through-hole 35 is about 45% to about 95% of the radius R₁ of the virtual spherical surface. It is preferable that a height h of the second through-hole 37 is about 20% to about 30% of the radius R₁ of the virtual spherical surface. To be more specific, the diameter d₁ of the first through-hole 36 is, e.g., 4.0 mm, the diameter d₂ of the second through-hole 37 is e.g., 7.0 mm, and the height h of the second through-hole 37 is, e.g., 2.5 mm. Due to these dimensions, the weight of the shoe 30 can be reduced by 30%, as compared with the conventional shoe 30 not having the through-hole 35.

Although the dimensions of the shoe 30 are described, the above numerical values are mere examples and the present invention is not limited thereto.

Next, an operation of this embodiment as structured above will be described.

At first, the drive unit (not shown), such as a motor, connected to the rotational shaft 2 drives the rotational shaft 2 in rotation (in the direction indicated by the arrow C in FIG. 1( a)). Since the rotational shaft 2 is driven to be rotated, the swash plate 5 provided on the rotational shaft 2 in an inclined manner is rotated (see FIG. 1( a)). At this time, the swash plate 5 is rotated in contact with the flat surface 32 of the shoe 30 located within the semispherical slide surface 13 of the piston 7 (see FIG. 1( a)).

Due to the rotation of the swash plate 5, the piston 7 is linearly moved in one direction of the rotational shaft direction (in the direction indicated by the arrow M₁ in FIG. 1( a)) (see FIG. 1( a)). At this time, the spherical surface 31 of the shoe 30 located within the semispherical slide surface 13 of the piston 7 is slid within the semispherical slide surface 13 of the piston 7 in a direction indicated by the arrow C₁ in FIG. 1( a) (see FIG. 1( a)).

During the linear movement of the piston 7 in the one rotational shaft direction, when a pressure of a frozen refrigerant compressed between the piston 7 and the second valve plate 8 b becomes greater than a pressure of a frozen refrigerant in the discharge pipe (not shown) connected to the second valve plate 8 b, the frozen refrigerant in the compression chamber 6 is discharged to the discharge pipe through the second discharge valve 21 b (see FIG. 1( a)). In addition, a frozen refrigerant containing a mist of lubrication oil is sucked from the suction pipe (not shown) into the compression chamber 6 through the first suction valve 22 a disposed on one end of the compression chamber 6 (see FIG. 1( a)). At this time, the first discharge valve 21 a provided in the first valve plate 8 a and the second suction valve 22 b provided in the second valve plate 8 b are closed (see FIG. 1( a)).

Then, the drive unit connected to the rotational shaft 2 further drives the rotational shaft 2 in rotation (in a direction indicated by the arrow C in FIG. 1( b)), so that the swash plate 5 provided on the rotational shaft 2 in an inclined manner is further rotated (see FIG. 1( b)). At this time, the swash plate 5 is rotated in contact with the flat surface 32 of the shoe 30 located within the semispherical slide surface 13 a of the piston 7 (see FIG. 1( b)).

Since the swash plate 5 is further rotated, the piston 7 is linearly moved in the other rotational shaft direction, i.e., in a direction opposed to the above direction (in a direction indicated by the arrow M₂ of FIG. 1( b)) (see FIG. 1( b)). At this time, the spherical surface 31 of the shoe 30 located within the semispherical slide surface 13 of the piston 7 is slid within the semispherical slide surface 13 of the piston 7 in a direction indicated by the arrow C₂ (see FIG. 1( b)).

During the linear movement of the piston 7 in the other rotational shaft direction, when a pressure of a frozen refrigerant compressed between the piston 7 and the first valve plate 8 a becomes greater than a pressure of a frozen refrigerant in the discharge pipe connected to the first valve plate 8 a, the frozen refrigerant in the compression chamber 6 is discharged to the discharge pipe through the first discharge valve 21 a (see FIG. 1( b)). In addition, a frozen refrigerant containing a mist of lubrication oil is sucked from the suction pipe into the compression chamber 6 through the second suction valve 22 b disposed in the other end of the compression chamber 6 (see FIG. 1( b)). At this time, the second discharge valve 21 b provided in the second valve plate 8 b and the first suction valve 22 a provided in the first valve plate 8 a are closed (see FIG. 1( b)).

Thereafter, the above steps are repeatedly carried out. As described above, since the rotational shaft 2 is rotated by the drive unit so that the swash plate 5 is rotated, the piston 7 can be reciprocated. Thus, the swash plate type compressor can compress a frozen refrigerant in the compression chamber 6 and discharge the compressed frozen refrigerant, as well as suck a frozen refrigerant from the suction pipe into the compression chamber 6.

While the piston 7 is being reciprocated, the lubrication oil passes through the cylindrical through-hole 35 communicating the flat surface 32 and the spherical surface 31 with each other, whereby the lubrication oil can be supplied to both of the flat surface 32 and the spherical surface 31 thoroughly (see FIG. 2). Thus, a frictional force generated between the spherical surface 31 of the shoe 30 and the semispherical slide surface 13 and a frictional force generated between the flat surface 32 of the shoe 30 and the swash plate 5 can be reduced. Thus, the seizure between the spherical surface 31 and the semispherical slide surface 13 can be prevented, and the seizure between the flat surface 32 and the swash plate 5 can be prevented.

In particular, when the operation of a general swash plate type compressor is started, since a frozen refrigerant flows at first, the inside of the swash plate type compressor is degreased so that no oil lubrication effect can be provided. Thus, the seizure between the shoe 30 and the swash plate 5 is likely to occur. On the other hand, according to this embodiment, owing to the provision of the through-hole 35, an oil, which was used before, remains in the through-hole 35. Namely, since the oil can be held in the through-hole 35, the seizure between the shoe 30 and the swash plate 5 can be securely prevented.

In addition, according to this embodiment, since the transitional hole 38 of a truncated conical shape is provided between the first through-hole 36 and the second through-hole 37, an oil can be easily stored. Thus, the seizure between the shoe 30 and the swash plate 5 can be more securely prevented.

In addition, according to this embodiment, since the cylindrical through-hole 37 having the second diameter d₂, which is relatively a larger diameter, is provided, a larger amount of remaining oil can be held. Thus, the seizure between the shoe 30 and the swash plate 5 can be more securely prevented.

In addition, as shown in FIG. 2, in this embodiment, since the first through-hole 36 and the second through-hole 37 have a cylindrical shape, and the first through-hole 36 and the second through-hole 37 are connected to each other through the transitional hole 38 of a truncated conical shape, a lubrication oil can smoothly flow between the flat surface 32 and the spherical surface 31. Thus, a frictional force generated between the spherical surface 31 and the semispherical slide surface 13, and a frictional force generated between the flat surface 32 and the swash plate 5, can be more securely reduced. As a result, the seizure between the spherical surface 31 and the semispherical slide surface 13, and the seizure between the flat surface 32 and the swash plate 5 can be more securely prevented. Meanwhile, in the embodiment shown in JP2002-39058A, since a lubrication oil pools in the hollow space, the lubrication oil cannot smoothly flow between the flat surface 32 and the spherical surface 31, unlike this embodiment. Therefore, the embodiment of the present invention is advantageous in this point, as compared with the invention disclosed in JP2002-39058A.

In addition, as shown in FIG. 2, in this embodiment, since the inner circumferential part of the flat surface 32 adjacent to the through-hole 35 is chamfered so as to be inclined toward the spherical surface 31, a lubrication oil on the flat surface 32 can be smoothly introduced to the through-hole 35. Similarly, the inner circumferential part of the spherical surface 31 adjacent to the through-hole 35 is chamfered so as to be inclined toward the flat surface 32, a lubrication oil on the spherical surface 31 can be smoothly introduced into the through-hole 35. From these structures, according to this embodiment, since a lubrication oil can be more smoothly moved between the flat surface 32 and the spherical surface 31, a frictional force generated between the spherical surface 31 and the semispherical slide surface 13, and a frictional force generated between the flat surface 32 and the swash plate 5, can be more securely reduced. As a result, the seizure between the spherical surface 31 and the semispherical slide surface 13, and the seizure between the flat surface 32 and the swash plate 5, can be more securely prevented.

In addition, as shown in FIG. 2, in this embodiment, since the through-hole 35 is provided, the weight of the shoe 30 can be reduced. More specifically, the weight of the shoe 30 can be reduced by 20% to 30%, as compared with the conventional shoe not having the through-hole 35. Thus, the rotation of the swash plate 5 can be accelerated, whereby the speed of the swash plate type compressor can be increased. When there is formed the shoe 30 having the shape shown in JP2002-39058A, the downsized shoe 30 cannot have a sufficient durability and such a shoe 30 cannot be practically used. On the other hand, according to this embodiment, the first through-hole 36 having the first diameter d₁, which is relatively a smaller diameter, is disposed on the side of the spherical surface 31 whose sectional area is smaller, and the second through-hole 37 having the second diameter d₂, which is relatively a larger diameter, is disposed on the side of the flat surface 32 whose sectional area is larger. Further, the transitional hole 38 of a truncated conical shape is formed between the first through-hole 36 and the second through-hole 37. Therefore, since the shoe 30 can be downsized while maintaining a certain or more thickness thereof, the shoe 30 can be more downsized while maintaining an excellent durability.

In addition, as shown in FIG. 2, in this embodiment, the spherical surface 31 has the non-contact surface 31 b which is not in contact with the semispherical slide surface 13 under the static state. Thus, a contact surface defined between the shoe 30 and the semispherical slide surface 13 of the piston 7 can be made smaller, whereby a frictional force generated between the shoe 30 and the semispherical slide surface 13 can be reduced. As a result, according to this embodiment, the shoe 30 can be more smoothly slid.

In addition, as described above, when the area of the contact surface 31 a of the spherical surface 31 and the area of the contact surface 32 a of the flat surface 32 are substantially equal to each other, a pressing force per unit area applied between the semispherical slide surface 13 and the spherical surface 31, and a pressing force per unit area applied between the flat surface 32 and the swash plate 5, can be made substantially equal to each other. Thus, the shoe 30 can be slid in a well-balanced manner.

Example

Next, a result of a friction and abrasion test (pin-on-disk friction and abrasion test) between the shoe 30 and the swash plate 5 is described.

A test apparatus shown in FIG. 4 is described. The test apparatus includes: a rotational shaft 61 which is only rotated without being moved in an axial direction; a pressurizing shaft 62 disposed with the rotational shaft 61, which is only moved in the axial direction without being rotated; shoe pressers 68 for pressing the shoe 30; and a swash plate fixing part 64 on which the swash plate 5 is fixed. The three shoe pressers 68 are located at equal circumferential intervals therebetween. The shoe pressers 68 are rotated together with the rotational shaft 61. The swash plate fixing part 64 is not to be rotated by a rotation stopper (not shown).

Disposed between the swash plate fixing part 64 and the pressurizing shaft 62 is a steel ball 63 serving as a pivot shaft. In addition, a protective barrel 65 for safety is disposed outward peripheries of the shoe pressers 68 and the swash plate fixing part 64.

An electric motor (not shown) for rotating the rotational shaft 61 is connected to the rotational shaft 61. The electric motor stops, when a rotational torque value exceeds a set value. Connected to the pressurizing shaft 62 is a pressurizing apparatus (not shown), such as an oil pressure generator, for loading and pressurizing the pressurizing shaft 62. A force in a torsional direction applied to the pressurizing shaft 62 is detected as a rotational torque value.

A frictional force was generated between the shoe 30 and the swash plate 5, by rotating the shoe 30 at a predetermined rotational speed, while pressing the slide surface 13 of the swash plate 5 onto the flat surface 32 of the shoe 30 by pressurizing the swash plate 5 in the upward direction in FIG. 4. To be more specific, the swash plate 5 was pressurized in the upward direction in FIG. 4 at forces of 50 kgf, 100 kgf, 150 kgf and 200 kgf, with the rotational speed of the rotational shaft 61 being maintained at 1000 rpm. Since the three shoe pressers 68 were located at the equal circumferential intervals therebetween, and the three shoes 30 were located, loads applied on each shoe 30 were respectively one third, i.e., 50/3 kgf, 100/3 kgf, 150/3 kgf and 200/3 kgf. In a general swash plate type compressor, a load applied to the shoe 30 is generally about 50 kgf.

Amounts of forces corresponding to the above frictional forces were detected as rotational torque values. The below-described Table 1 shows these values. The rotational torque value corresponds to the performance of the shoe 30 with respect to the swash plate 5. When the rotational torque value is small, the seizure rarely occurs, i.e., the performance of the shoe 30 is excellent.

As a comparative example, there was used the conventional shoe 30 not having the through-hole 35.

TABLE 1 period (sec) load (kgf) 0 60 120 180 240 300 Comparative 50 0.5 0.5 0.5 0.5 0.5 0.5 Example 100 0.5 0.9 0.8 0.8 0.7 0.7 Shoe 150 1.5 1.7 1.8 1.9 1.9 2.0 200 2.0 2.0 2.3 2.4 2.5 2.5 Example 50 0.7 0.5 0.5 0.5 0.5 0.5 Shoe 100 1.5 0.8 0.8 0.8 0.75 0.75 150 1.8 1.1 1.2 0.7 0.7 0.7 200 2.0 1.3 1.0 0.75 0.7 0.65

As understood from the above Table 1, there is not so remarkable difference between the comparative example shoe and the example shoe, in the regions of 50 kgf and 100 kgf as low loads. On the other hand, in the regions of 150 kgf and 200 kgf as high loads, the rotational torque values of the example shoe 30 are less than the rotational torque values of the comparative example shoe. Thus, it can be understood that the example shoe is excellent against friction and abrasion. In particular, after 300 seconds had passed with a load of 200 kgf being applied, the rotational torque value of the comparative example shoe was 2.5, while the rotational torque value of the example shoe was 0.65. Namely, the rotational torque value of the comparative example shoe is 3.8 times (=2.5/0.65) the rotational torque value of the example shoe. Thus, it can be understood that the example shoe 30 can be expected to provide a seizure prevention effect which is about four times a seizure prevention effect provided by the comparative example shoe.

-   1 a, 1 b cylinder block -   2 rotational shaft -   5 swash plate -   7 piston -   8 a first valve plate -   8 b second valve plate -   20 housing -   30 shoe -   31 spherical surface -   32 flat surface -   35 through-hole -   36 first through-hole -   37 second through-hole -   38 transitional hole 

1. A shoe for swash plate type compressor, disposed between a swash plate provided on a rotational shaft in an inclined manner, the swash plate being configured to be rotated together with the rotational shaft, and a piston configured to be reciprocated in a direction in which the rotational shaft extends, by means of the rotation of the swash plate, the shoe for swash plate type compressor comprising: a flat surface in contact with the swash plate; and a spherical surface in contact with a semispherical slide surface formed on the piston; wherein: a through-hole communicating the flat surface and the spherical surface with each other is formed between the flat surface and the spherical surface; and the through-hole is composed of a first through-hole of a cylindrical shape having a first diameter and a second through-hole of a cylindrical shape having a second diameter that is larger than the first diameter.
 2. The shoe for swash plate type compressor according to claim 1, wherein the first through-hole is formed on a side of the spherical surface so as to extend up to the spherical surface, and the second through-hole is formed on a side of the flat surface so as to extend up to the flat surface.
 3. The shoe for swash plate type compressor according to claim 1, further comprising a transitional hole of a truncated conical shape formed between the first through-hole and the second through-hole, the transitional hole communicating the first through-hole and the second through-hole with each other.
 4. The shoe for swash plate type compressor according to claim 1, wherein an inner circumferential part of the flat surface adjacent to the through-hole is inclined toward the spherical surface, and an inner circumferential part of the spherical surface adjacent to the through-hole is inclined toward the flat surface.
 5. The shoe for swash plate type compressor according to claim 1, wherein the spherical surface has a contact surface in contact with the slide surface of the piston under a static state, and a non-contact surface not in contact with the slide surface under the static state.
 6. The shoe for swash plate type compressor according to claim 5, wherein the flat surface has a contact surface in contact with the swash plate under the static state, and an area of the contact surface of the spherical surface and an area of the contact surface of the flat surface are substantially equal to each other. 